JPS63100919A - Purifying method for exhaust gas and catalyst - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and a catalyst for efficiently removing nitrogen oxides from exhaust gases emitted from internal combustion engines such as automobiles, nitric acid manufacturing plants, etc.

[Conventional technology]

In recent years, exhaust gases emitted from internal combustion engines such as automobiles, nitric acid manufacturing factories, etc. contain harmful components such as nitrogen oxides (NO), which are causing air pollution. Therefore, the removal of nitrogen oxides from this exhaust gas has been extensively studied.

Conventionally, as a method for removing nitrogen oxides, there is a catalyst removal method in which exhaust gas is brought into contact with a catalyst. In this method, nitrogen oxides in the exhaust gas are adsorbed onto the catalyst surface, and the nitrogen oxides are dissociated into nitrogen and oxygen. At the same time, the dissociated oxygen is reacted with a reducing agent such as carbon oxide or hydrogen, and finally all nitrogen oxides are removed.

As the catalyst for removing nitrogen oxides in the above conventional technology,
Copper, bacdium, and platinum on a carrier made of porous materials such as amina, zirconia, and zeolite.

A metal supporting metal such as rhodium is used, however, after washing with the conventional method, reducing substances such as ammonia, carbon oxide, and hydrogen are completely oxidized to form water (HxO).
In a state in which oxygen is present in excess of the amount of oxygen necessary for conversion into carbon dioxide (cOz), that is, in an oxidizing atmosphere, oxygen and reducing substances preferentially react with each other. Therefore, the oxygen dissociated from the nitrogen oxides cannot react with the reducing substance, and the dissociation (removal) of the nitrogen oxides does not proceed.

For example, in the case of automobile exhaust gas, when the ratio of air to fuel (air-fuel ratio) increases, it contains more oxygen than is necessary to completely burn the unburned components, and this oxidation The atmosphere does not promote the removal of nitrogen oxides as described above.

[Purpose of the invention]

The present invention aims to solve the above-mentioned conventional problems and provide a method and a catalyst for efficiently removing nitrogen oxides in an oxidizing atmosphere.

[Structure of the invention]

The exhaust gas purification method of the first invention includes preparing a catalyst containing copper, and bringing nitrogen oxide-containing exhaust gas into contact with the catalyst in an oxidizing atmosphere in the presence of hydrocarbons to oxidize nitrogen in the exhaust gas. It is characterized by the removal of objects.

The exhaust gas purification method of the second invention comprises first bringing the exhaust gas containing nitrogen oxides into contact with a catalyst containing copper in the presence of hydrocarbons in an oxidizing atmosphere, and then bringing the exhaust gas into contact with the oxidation catalyst.・It is characterized by removing nitrogen oxides from exhaust gas.

Further, the exhaust gas purification catalyst of the third invention is a catalyst for removing nitrogen oxides in exhaust gas in an oxidizing atmosphere,
It is characterized by supporting copper on a porous carrier such as alumina, silica, or zeolite.

The present invention will be explained in detail below.

The present invention is based on the discovery that a copper-containing catalyst selectively promotes the reaction between nitrogen oxides and hydrocarbons in exhaust gas in an oxidizing atmosphere.

The exhaust gas purifying catalyst according to the present invention contains copper (al), and the copper is supported on a porous carrier.

Examples of the porous carrier include alumina and silica.

Examples include silica 7 gelumina and zeolite, and one or more of these may be used. Further, the shape of the porous carrier includes zero grain shape, non-uniform shape, and the like.

The amount of copper supported on the porous carrier is preferably within the range of 0.1 to 50f per 1eK of the porous carrier. If the supported amount is less than 0.1f, the above effect cannot be obtained.<<, 5a
Even if the amount exceeds y, an effect commensurate with the amount supported cannot be obtained.

In addition, as a method for supporting the porous carrier Edo, 9
It is preferable to do this as follows.

That is, p-copper compounds such as nitrates and acetates in water.

The porous carrier is dissolved in a solvent such as alcohol, and the porous carrier is immersed in the solution to impregnate the carrier with the solution.

Next, by heating after drying, copper is impregnated and supported in the above-mentioned carrier.

Removal of nitrogen acids and arsenics from exhaust gas is carried out by using the copper-containing catalyst and bringing the exhaust gas into contact with the catalyst in an oxidizing atmosphere in the presence of hydrocarbons.

The above oxidizing atmosphere refers to carbon monoxide contained in exhaust gas,
The amount of oxygen required to completely oxidize the reducing substance of the hydrocarbon added in the hydrogen and hydrocarbon and zero treatment and convert it into HxO and Co indicates a state in which an excess of oxygen is included. For example, in the case of exhaust gas emitted from internal combustion engines such as automobiles.

The air-fuel ratio is in a high state (lean region).

In this oxidizing atmosphere, the copper-containing agent reacts not only with hydrocarbons and oxygen, but also with hydrocarbons (HC) and nitrogen oxides (NOx) (as shown in the equation below). It preferentially accelerates and removes nitrogen oxides.

uHc+ vNOx 4wH*0 + yCO2+ Z
Hydrocarbons remaining in the exhaust gas may be used as the hydrocarbons to make Nt exist, but if the amount is insufficient than necessary to cause the above reaction or if the exhaust gas does not contain any hydrocarbons, .

It is better to add hydrocarbons from outside. Note that the reaction is more accelerated when the amount of hydrocarbon is in excess of the required amount.

The amount of the hydrocarbon present is 100 to 5000 p
pm (concentration when converted to On) is desirable.

In addition, copper-containing catalysts have a high activity for removing nitrogen oxides, but have a low activity for oxidizing carbon monoxide (00), hydrogen F, etc. contained in exhaust gas, so they can also remove the above-mentioned carbon oxides, hydrocarbons, etc. K to remove etc.

After the nitrogen oxides are removed, the exhaust gas may be brought into contact with the oxidation catalyst.

Examples of the oxidation catalyst include Pt, Pd, Rh, etc., and one or more of these may be used. Nucleic oxidation catalysts are alumina and silica.

It is best to use it supported on a porous carrier such as zirconia.
In this case, the supported amount of the oxidation catalyst is as follows:
', preferably within the range of 0.1 to 10 da. If the supported amount is less than 0.1f, the above effect cannot be obtained.
(Also, even if the amount exceeds 10, the effect cannot be improved commensurate with the amount supported.

As an example embodying the exhaust gas purification method of the present invention, the copper-containing catalyst is placed in one reactor.

Instead of introducing the exhaust gas into the reactor, there is a method of bringing the copper-containing catalyst into contact with the exhaust gas, and then taking out the purified exhaust gas from the reactor. This ■.

The reactor is provided with an oxidizing atmosphere, and if the amount of hydrocarbons is insufficient, hydrocarbons are supplied into the reactor.

Furthermore, as an example of a method for purifying exhaust gas using a copper-containing catalyst and an oxidation catalyst, a reactor in which a copper-containing catalyst is arranged and a reactor in which an oxidation catalyst is arranged are prepared. There is a method in which the reactor is placed on the upstream side of the exhaust gas (first stage) K, and the reactor for the oxidation catalyst is placed on the downstream side (second stage) K. Further, as a catalyst used in this method, there is one in which copper is supported on the exhaust gas inflow side of a monolithic carrier (integrated carrier) and an oxidation catalyst is supported on the exhaust gas outflow side of the carrier. With this catalyst, it is possible to remove nitrogen oxides and hydrocarbons and carbon oxides from exhaust gas using a single carrier.

The reaction temperature of catalyst ii consisting of the copper-containing catalyst is 3
The temperature is preferably within the range of 00 to 600°C.

Further, when an oxidation catalyst is used, the reaction temperature of the catalyst layer is preferably in the range of 200 to 800°C.

In addition, the space velocity (SV) for introducing exhaust gas into the catalyst layer is 1 when introducing it into the catalyst layer of a copper-containing catalyst.
,000 to 10,000 hr, and 1. (100~10,000hr'
It is preferably within the range of .

Further, when purifying exhaust gas from an internal combustion engine such as an automobile, it is preferable to arrange a copper-containing catalyst or an oxidation catalyst together with the copper-containing catalyst downstream of the exhaust manifold.

Further, both the copper-containing catalyst and the oxidation catalyst according to the present invention are 9 granular bodies, verves, torso-shaped bodies, 82 cam-shaped bodies, etc.

Its shape and structure do not matter.

Note that the present invention can be used not only for internal combustion engines such as automobiles, but also for purifying exhaust gas containing nitrogen oxides from nitric acid manufacturing plants, various combustion equipment, and the like.

[Operation and effect of the invention]

According to the present invention, it is possible to provide a method and a catalyst that can remove nitrogen acids and arsenides from exhaust gas with high efficiency in an oxidizing atmosphere where oxygen is present in excess.

This is because the copper-containing catalyst according to the present invention preferentially promotes the reaction between nitrogen oxides and hydrocarbons in the presence of hydrocarbons.

Further, by further contacting the exhaust gas from which nitrogen oxides have been removed using the copper-containing catalyst with the oxidation catalyst, unreacted CO and HC can be oxidized and removed.

〔Example〕

The present invention will be described in detail below.

Example 1 First, a copper-containing catalyst according to the present invention was prepared as follows.

100 cc of 0.5 moe/(l copper nitrate aqueous solution at 80°C
KY type zeolite (manufactured by Union Carbide) 5Qe
After soaking for 24 hours, it was washed with water. This operation was repeated 5 times, dried at 110°C for 12 hours, and then calcined at 600°C in air for 3 hours to produce a catalyst according to the present invention (sample ratio 1).
@Nao prepared this.

The amount of copper supported in the catalyst was 2 wt%.

For comparison, a comparative catalyst (sample ff1cl) in which palladium was supported was prepared by immersing the same zeophyte as above in a nitric acidic aqueous solution of palladium nitrate, drying and firing in the same manner as above. The amount of palladium supported in the catalyst was 0.2 wt%.Next, for the above two types of catalysts, K HC
The selectivity of the -NOx reaction and the HO-ox reaction was investigated.

A quartz reactor (fixed bed flow type) K having an inner diameter of 18 tl was filled with 7 cc of catalyst. The catalyst layer was heated to 400°C and NOlooooppm and Ox were heated at a space velocity (8V) for 30,000 hours.
A 2% mix ON, balance gas was introduced into the reactor. At the same time, the trap was filled with propylene. No and O7 at that time
The conversion rate was measured. The results are shown in the figure. Propylene introduced into the 0 reactor increases from left to right in the figure (prop), and the diagonal line indicates that the selectivity between the HC-No reaction and the HC-○ mushroom reaction is 50%.

As shown in the figure, when the catalyst according to the example (sample ratio 1) is used, it is located far above the diagonal line.

It can be seen that the selectivity of the HC-NOx reaction is excellent.

In contrast, when the comparative catalyst (sample hc1) was used, 0. Located on the axis of conversion rate, mostly HC-N
It can be seen that the O== reaction does not occur.

Example 2. .

Sample ratios 2 to 5 of this example were prepared by impregnating the porous carrier shown in the table with a copper nitrate aqueous solution and using a conventional method. Comparative catalyst samples kc2-C supporting the metals shown in the table for comparison
5 was prepared similarly.

The reaction is as in Example 1. under the same equipment conditions.

NO: 11000PP, CO: 0.3%, propylene 1
300 ppm (THC concentration), 01:2.1%,
C.O.

: 12%, H, O: 3%, balance N. (2) The conversion rate of NO was measured by touching the gas. The results are shown in the table.

It can be seen from the table that the catalyst of the example has a higher NO conversion rate than the comparative catalyst.

Example 3 In this example, actual engine exhaust is used! 7No. ① Conversion rate was investigated.

Catalyst sample ratio 1 of Example 1 was changed to 1.9e catalyst con)<,y
- Fill the 200 cc engine with air-fuel ratio A/F.
=18 (Lean) 9 rotation speed 160Orpm.

? = * -A/de operated at negative pressure 400 mHg, N
The O, O conversion rate was measured. The inflow temperature of exhaust gas into the catalytic converter is 400°C, and the concentration of NO is 150°C.
It was 0 ppm. The NO-conversion rate at that time was 40%, and when the catalyst sample C1 of Example 1 was similarly tested as a comparative example, NO1 did not decrease at all (the conversion rate was 0).
%).

As described above, it can be seen that the exhaust gas purification method according to the present invention can efficiently purify NOj in an oxidizing atmosphere where oxygen is present in excess.

Example 4 In this example, upstream (front) Kou of the actual engine exhaust flow
An oxidation catalyst is installed downstream (backward) of the @ medium, and NO,
, Co, and HC were investigated.

Fill a 1.9e catalyst converter with the catalyst sample volume 1 of Example 1, and place the catalyst sample volume 1 of Example 1 on the exhaust manifold side.
Fill kC1 into 1.9e catalyst compagu and install it. After that, the 200 cc engine was set to A/F=18.
(Lean) 0 rpm before 2000r, manifold negative pressure 3
Operate at 50 mHg.

NOx, CO, HC! The conversion rate was measured. The temperature at which exhaust gas flows into the catalytic converter is 500°C.

NO,■ concentration is 2000 pPm, co concentration is 0.2
%.

The T'HO concentration was 1500 PPm.
O! Conversion rate is 45%, CO conversion rate is 99%, HC゛-
The conversion rate of No. 1 was 98%.

As a comparative example, the catalyst sample Arashi C1 of Example 1 was used as a catalyst sample? !
When the same experiment was carried out with 1c filled instead of 1L1, no. −,,,m+iS°,. . ,. . □, it was the same as the example.

As described above, it can be seen that the exhaust gas purification method according to the present invention can efficiently purify NOx in an oxidizing atmosphere where oxygen is present in excess.

Example 5 In this example, a catalyst was prepared in which a monolithic carrier supported a Kou catalyst in the former part and Pd, which is an acid catalyst, in the latter part.
The conversion rates of O, CO, and He were investigated.

Mohas carrier made of cordierite (400)<- (manufactured by Nippon Insulator, diameter 50 m7'md, length 5 parts m/m.

The front section (approximately 25 m/m ) of KY type zeolite (Union Carbide P!A8 K) weighs approximately 15 g.
-40) 80 parts and 8sankagaku aluminium/'(A8
200) 20 parts were mixed and made into a slurry.
, and fired at 500°C. The amount of coating on the carrier is approximately 2.5g
Met.

A slurry prepared by mixing 80 parts of r-alumina powder (pulverized KIIA-24 manufactured by Sumitomo Chemical Co., Ltd.) and 20 parts of the alumina/I was coated on the latter part of the monolithic carrier in the same manner as above. The amount of coating on the carrier was about 3 g.

Loading of Cu on the front stage was carried out in the same manner as in the catalyst stage 1 of Example 1. Further, Pd was supported on the latter part in the same manner as in the comparison catalyst NzC1 of Example 1. The amount of supported catalyst components is 0.24 wt% for O and 0.03 w for Pd.
It was t%.

:2,5 ril. Gases containing COt: 10%, Hid: 1 part %, and the balance N2 were introduced at a flow rate of 50 e/min into a trap-heated catalyst at 500°C. At that time, the NO conversion rate was 30%, CO
The conversion rate was 98%, and the propylene conversion rate was 99%.

For comparison, only the rear stage section of the catalyst was cut out, and the experiment was conducted in the same manner as above using the latter section.

The No conversion rate was 0% and the CO conversion rate was 95%.

The propylene conversion rate was 96%.

As described above, it can be seen that the exhaust gas purification method according to the present invention can efficiently purify NO in an oxidizing atmosphere trap where oxygen is present in excess.

[Brief explanation of the drawing]

The figure is a diagram showing the NO, conversion rate, and O2 conversion rate in Example 1.

Claims (4)

[Claims] (1) Nitrogen oxides in the exhaust gas are removed by preparing a catalyst containing copper and bringing the exhaust gas containing nitrogen oxides into contact with the catalyst in the presence of hydrocarbons in an oxidizing atmosphere. Exhaust gas purification method. (2) Nitrogen oxides in the exhaust gas are removed by bringing the exhaust gas containing nitrogen oxides into contact with a copper-containing catalyst in the presence of hydrocarbons in an oxidizing atmosphere, and then bringing the exhaust gas into contact with an oxidation catalyst. An exhaust gas purification method characterized by removing. (3) An exhaust gas purification catalyst for removing nitrogen oxides from exhaust gas in an oxidizing atmosphere, characterized in that copper is supported on a porous carrier such as alumina, silica, or zeolite. (4) Exhaust gas purification according to claim (3), wherein the porous carrier is a monolithic carrier, copper is supported on the front part of the monolithic carrier, and an oxidation catalyst is supported on the rear part of the monolithic carrier. catalyst.